In general, moving images for preview are displayed on a display unit in a digital camera. When a desired subject to be photographed is in the displayed moving images, the user presses a shutter button to shoot the subject as a still image.
In a digital camera, if an image to be shot has many pixels, it takes a lot of time to read out an image signal from an image sensor and to perform image processing on the image signal. Because of this, if the number of pixels of a moving image for a preview is similar to the number of pixels of a still image, a possibility arises in which an operation of the digital camera will be delayed.
Thus, when the digital camera shoots a still image, a drive mode of the image sensor needs to be switched from a moving image mode for shooting a moving image for a preview to a still image shooting mode for shooing a still image in which having the number of pixels Is greater than that of the moving image.
A technique for switching a moving image mode and a still image shooting mode has already been proposed.
FIG. 1 is a time chart illustrating an operation of a digital camera for which a technique like this is used. The digital camera is operated in a moving image mode, and then, a shutter button is pressed for switching to a still image shooting mode.
An image sensor of the digital camera stores charges by making an exposure (expose 42) and outputs (sensor output 41) the charges as an image signal (image 1). An ISP (Image Signal Processor) captures the image signal (capture 44). The ISP performs image processing on the captured image signal and outputs the image signal in which the image processing has been preformed (ISP output 45). The image signal is displayed on a monitor.
Additionally, the image sensor starts an exposure for shooting a next image signal (image 2) when outputting the image signal (image 1).
When the shutter button is pressed (press shutter 47) while exposing the image signal (image 2), the digital camera initially stops displaying the image signal on the monitor (internal processing 46 (stop monitor)). The exposure and the output of the image signal by the image sensor are performed even while the digital camera stops displaying the image signal on the monitor.
Next, the digital camera switches the moving image mode to the still image shooting mode (internal processing 46 (switch)) and causes the image sensor to start an exposure for a still image (image 5). After that, when a predetermined time passes, the digital camera closes the mechanical shutter to end the exposure (mechanical shutter 43 (close)) and outputs images stored by the exposure.
However, if the exposure is started after the drive mode of the image sensor has been switched, it takes a lot of time to start the exposure after the shutter button has been pressed. Because of this, the user may not capture an image of a desired subject.
In Patent document 1 (Japanese Patent Laid-Open No. 2000-23016), a digital camera capable of reducing time from pressing the shutter button to starting the exposure is disclosed.
This digital camera includes a first CCD sensor and a second CCD sensor in which the number of pixels is greater than that of the first CCD sensor. In the moving image mode, the first CCD sensor captures a moving image and the moving image is displayed on an LCD. When a shutter button is pressed during a live view, the second CCD sensor starts shooting the still image.
Because of this, switching the drive mode of the image sensor is not necessary so that the time from pressing the shutter button to starting a shot can be reduced.    Patent document 1: Japanese Patent Laid-Open No. 2000-23016
Recently, mobile terminals such as mobile phones often include digital cameras. Because of this, downsizing digital cameras is required.
Like the digital camera disclosed in Patent document 1, when a dedicated sensor for shooting a still image is provided in addition to besides a dedicated sensor for shooting a moving image, the digital camera becomes larger. Additionally, it is possible to remove a function that displays the moving image for previewing it from the digital camera and to shoot a desired subject through the finder (window for confirming a composition). In this case, the digital camera also becomes larger.
An object of the present invention is to provide an image processing circuit, a mobile terminal and a method for controlling a sensor, which are capable of shooting a desired subject but which does not lead to an increase in the size of the digital camera.